Network Working Group L. Zheng
Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies
Expires: November 30,December 4, 2014 M. Bhatia
Alcatel-Lucent
May 29,June 2, 2014
LDP Hello Cryptographic Authentication
draft-ietf-mpls-ldp-hello-crypto-auth-07.txtdraft-ietf-mpls-ldp-hello-crypto-auth-08.txt
Abstract
This document introduces a new optional Cryptographic Authentication
TLV that LDP can use to secure its Hello messages. It secures the
Hello messages against spoofing attacks and some well known attacks
against the IP header. This document describes a mechanism to secure
the LDP Hello messages using National Institute of Standards and
Technology (NIST) Secure Hash Standard family of algorithms.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 30,December 4, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Cryptographic Authentication TLV . . . . . . . . . . . . . . 4
2.1. Optional Parameter for Hello Message . . . . . . . . . . 4
2.2. LDP Security Association . . . . . . . . . . . . . . . . 4
2.3. Cryptographic Authentication TLV Encoding . . . . . . . . 6
2.4. Sequence Number Wrap . . . . . . . . . . . . . . . . . . 8
3. Cryptographic Authentication Procedure . . . . . . . . . . . 8
4. Cross Protocol Attack Mitigation . . . . . . . . . . . . . . 8
5. Cryptographic Aspects . . . . . . . . . . . . . . . . . . . . 8
5.1. Preparing the Cryptographic Key . . . . . . . . . . . . . 9
5.2. Computing the Hash . . . . . . . . . . . . . . . . . . . 9
5.3. Result . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Processing Hello Message Using Cryptographic Authentication . 10
6.1. Transmission Using Cryptographic Authentication . . . . . 10
6.2. Receipt Using Cryptographic Authentication . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 1213
10.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 1314
1. Introduction
The Label Distribution Protocol (LDP) [RFC5036] sets up LDP sessions
that run between LDP peers. The peers could either be directly
connected at the link level or could be multiple hops away. An LDP
Label Switching Router (LSR) could either be configured with the
identity of its peers or could discover them using LDP Hello
messages. These messages are sent encapsulated in UDP addressed to
"all routers on this subnet" or to a specific IP address. Periodic
Hello messages are also used to maintain the relationship between LDP
peers necessary to keep the LDP session active.
Since the Hello messages are sent using UDP and not TCP, these
messages cannot use the security mechanisms defined for TCP
[RFC5926]. While some configuration guidance is given in [RFC5036]
to help protect against false discovery messages, it does not provide
an explicit security mechanism to protect the Hello messages.
Spoofing a Hello packet for an existing adjacency can cause the valid
adjacency to time out and in turn can result in termination of the
associated session. This can occur when the spoofed Hello specifies
a smaller Hold Time, causing the receiver to expect Hellos within
this smaller interval, while the true neighbor continues sending
Hellos at the previously agreed lower frequency. Spoofing a Hello
packet can also cause the LDP session to be terminated directly,
which can occur when the spoofed Hello specifies a different
Transport Address, other than the previously agreed one between
neighbors. Spoofed Hello messages have been observed and reported as
a real problem in production networks [RFC6952].
For Link Hello, [RFC5036] states that the threat of spoofed Hellos
can be reduced by accepting Hellos only on interfaces to which LSRs
that can be trusted are directly connected, and ignoring Hellos not
addressed to the "all routers on this subnet" multicast group. The
Generalized TTL Security Mechanism (GTSM) provides a simple and
reasonably robust defense mechanism for Link Hello [RFC6720], but it
does not secure against packet spoofing attack or replay
attack[RFC5082].
Spoofing attacks via Targeted Hellos are a potentially more serious
threat. [RFC5036] states that an LSR can reduce the threat of
spoofed Targeted Hellos by filtering them and accepting only those
originating at sources permitted by an access list. However,
filtering using access lists requires LSR resource, and does not
prevent IP-address spoofing.
This document introduces a new Cryptographic Authentication TLV which
is used in LDP Hello messages as an optional parameter. It enhances
the authentication mechanism for LDP by securing the Hello message
against spoofing attack. It also introduces a cryptographic sequence
number carried in the Hello messages that can be used to protect
against replay attacks. The LSRs could be configured to only accept
Hello messages from specific peers when authentication is in use.
Using this Cryptographic Authentication TLV, one or more secret keys
(with corresponding Security Association (SA) IDs) are configured in
each system. For each LDP Hello message, the key is used to generate
and verify a HMAC Hash that is stored in the LDP Hello message. For
cryptographic hash function, this document proposes to use SHA-1,
SHA-256, SHA-384, and SHA-512 defined in US NIST Secure Hash Standard
(SHS) [FIPS-180-3]. The HMAC authentication mode defined in
[RFC2104] is used. Of the above, implementations MUST include
support for at least HMAC-SHA-256 and SHOULD include support for
HMAC-SHA-1 and MAY include support for either of HMAC-SHA-384 or
HMAC-SHA-512.
2. Cryptographic Authentication TLV
2.1. Optional Parameter for Hello Message
[RFC5036] defines the encoding for the Hello message. Each Hello
message contains zero or more Optional Parameters, each encoded as a
TLV. Three Optional Parameters are defined by [RFC5036]. This
document defines a new Optional Parameter: the Cryptographic
Authentication parameter.
Optional Parameter Type
------------------------------- --------
IPv4 Transport Address 0x0401 (RFC5036)
Configuration Sequence Number 0x0402 (RFC5036)
IPv6 Transport Address 0x0403 (RFC5036)
Cryptographic Authentication TBD1 (this document, TBD1 by IANA)
The Cryptographic Authentication TLV Encoding is described in section
2.3.
2.2. LDP Security Association
An LDP Security Association (SA) contains a set of parameters shared
between any two legitimate LDP speakers.
Parameters associated with an LDP SA are as follows:
o Security Association Identifier (SA ID)
This is a 32-bit unsigned integer used to uniquely identify an LDP
SA between two LDP peers, as manually configured by the network
operator (or, in the future, possibly by some key management
protocol specified by the IETF) .
The receiver determines the active SA by looking at the SA ID
field in the incoming Hello message.
The sender, based on the active configuration, selects an SA to
use and puts the correct SA ID value associated with the SA in the
LDP Hello message. If multiple valid and active LDP SAs exist for
a given interface, the sender may use any of those SAs to protect
the packet.
Using SA IDs makes changing keys while maintaining protocol
operation convenient. Each SA ID specifies two independent parts,
the authentication algorithm and the authentication key, as
explained below.
Normally, an implementation would allow the network operator to
configure a set of keys in a key chain, with each key in the chain
having fixed lifetime. The actual operation of these mechanisms
is outside the scope of this document.
Note that each SA ID can indicate a key with a different
authentication algorithm. This allows the introduction of new
authentication mechanisms without disrupting existing LDP
sessions.
o Authentication Algorithm
This signifies the authentication algorithm to be used with the
LDP SA. This information is never sent in clear text over the
wire. Because this information is not sent on the wire, the
implementer chooses an implementation specific representation for
this information.
Currently, the following algorithms are supported:
HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512.
o Authentication Key
This value denotes the cryptographic authentication key associated
with the LDP SA. The length of this key is variable and depends
upon the authentication algorithm specified by the LDP SA.
o KeyStartAccept
The time that this LDP router will accept packets that have been
created with this LDP Security Association.
o KeyStartGenerate
The time that this LDP router will begin using this LDP Security
Association for LDP Hello message generation.
o KeyStopGenerate
The time that this LDP router will stop using this LDP Security
Association for LDP Hello message generation.
o KeyStopAccept
The time that this LDP router will stop accepting packets
generated with this LDP Security Association.
In order to achieve smooth key transition, KeyStartAccept SHOULD be
less than KeyStartGenerate and KeyStopGenerate SHOULD be less than
KeyStopAccept. If KeyStartGenerate or KeyStartAccept are left
unspecified, the time will default to 0 and the key will be used
immediately. If KeyStopGenerate or KeyStopAccept are left
unspecified, the time will default to infinity and the key's lifetime
will be infinite. When a new key replaces an old, the
KeyStartGenerate time for the new key MUST be less than or equal to
the KeyStopGenerate time of the old key. Any unspecified values are
encoded as Zero.
Key storage SHOULD persist across a system restart, warm or cold, to
avoid operational issues. In the event that the last key associated
with an interface expires, it is unacceptable to revert to an
unauthenticated condition, and not advisable to disrupt routing.
Therefore, the router SHOULD send a "last Authentication Key
expiration" notification to the network manager and treat the key as
having an infinite lifetime until the lifetime is extended, the key
is deleted by network management, or a new key is configured
2.3. Cryptographic Authentication TLV Encoding
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Auth (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Security Association ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptographic Sequence Number (High Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptographic Sequence Number (Low Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Type: TBD1, Cryptographic Authentication
- Length: Specifying the length in octets of the value field.
- Security Association ID: 32 bit field that maps to the
authentication algorithm and the secret key used to create the
message digest carried in LDP payload.
Though the SA ID implies the algorithm, the HMAC output size should
not be used by implementers as an implicit hint, because additional
algorithms may be defined in the future that have the same output
size.
- Cryptographic Sequence Number: 64-bit strictly increasing sequence
number that is used to guard against replay attacks. The 64-bit
sequence number MUST be incremented for every LDP Hello packet sent
by the LDP router. Upon reception, the sequence number MUST be
greater than the sequence number in the last LDP Hello packet
accepted from the sending LDP neighbor. Otherwise, the LDP packet is
considered a replayed packet and dropped.
LDP routers implementing this specification MUST use existing
mechanisms to preserve the sequence number's strictly increasing
property for the deployed life of the LDP router (including cold
restarts). One mechanism for accomplishing this could be to use the
high-order 32 bits of the sequence number as a boot count that is
incremented anytime the LDP router loses its sequence number state.
Techniques such as sequence number space partitioning described above
or non-volatile storage preservation can be used but are beyond the
scope of this specification. Sequence number wrap is described in
Section 2.4.
- Authentication Data:
This field carries the digest computed by the Cryptographic
Authentication algorithm in use. The length of the Authentication
Data varies based on the cryptographic algorithm in use, which is
shown as below:
Auth type Length
--------------- ----------
HMAC-SHA1 20 bytes
HMAC-SHA-256 32 bytes
HMAC-SHA-384 48 bytes
HMAC-SHA-512 64 bytes
2.4. Sequence Number Wrap
When incrementing the sequence number for each transmitted LDP
packet, the sequence number should be treated as an unsigned 64-bit
value. If the lower order 32-bit value wraps, the higher order
32-bit value should be incremented and saved in non-volatile storage.
If the LDP router is deployed long enough that the 64-bit sequence
number wraps, all keys, independent of key distribution mechanism
MUST be reset. This is done to avoid the possibility of replay
attacks. Once the keys have been changed, the higher order sequence
number can be reset to 0 and saved to non-volatile storage.
3. Cryptographic Authentication Procedure
As noted earlier, the Security Association ID maps to the
authentication algorithm and the secret key used to generate and
verify the message digest. This specification discusses the
computation of LDP Cryptographic Authentication data when any of the
NIST SHS family of algorithms is used in the Hashed Message
Authentication Code (HMAC) mode.
The currently valid algorithms (including mode) for LDP Cryptographic
Authentication include:
HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512
Of the above, implementations of this specification MUST include
support for at least HMAC-SHA-256 and SHOULD include support for
HMAC-SHA-1 and MAY also include support for HMAC-SHA-384 and HMAC-
SHA-512.
Implementations of this standard MUST use HMAC-SHA-256 as the default
authentication algorithm.
4. Cross Protocol Attack Mitigation
In order to prevent cross protocol replay attacks for protocols
sharing common keys, the two octet LDP Cryptographic Protocol ID is
appended to the authentication key prior to use (refer to Section 8).
Other protocols using the common key similarly append their own
Cryptographic Protocol IDs to their keys prior to use thus ensuring
that a different key value is used for each protocol.
5. Cryptographic Aspects
In the algorithm description below, the following nomenclature is
used:
H is the specific hashing algorithm (e.g. SHA-256).
K is the Authentication Key from the LDP security association.
Ks is a Protocol Specific Authentication Key obtained by appending
Authentication Key (K) with the two-octet LDP Cryptographic Protocol
ID .
Ko is the cryptographic key used with the hash algorithm.
L is the length of the hash, measured in octets rather than bits.
AuthTag is a value which is the same length as the hash output. In
case of IPv4, the first 4 octets contain the IPv4 source address
followed by the hexadecimal value 0x878FE1F3 repeated (L-4)/4 times.
In case of IPv6, the first 16 octets contain the IPv6 source address
followed by the hexadecimal value 0x878FE1F3 repeated (L-16)/4 times.
This implies that hash output is always a length of at least 16
octets.
5.1. Preparing the Cryptographic Key
The LDP Cryptographic Protocol ID is appended to the Authentication
Key (K) yielding a Protocol Specific Authentication Key (Ks). In
this application, Ko is always L octets long. Keys that are longer
than the bit length of the hash function are hashed to force them to
this length, as we describe below. Ks is computed as follows:
If the Protocol Specific Authentication Key (Ks) is L octets long,
then Ko is equal to Ks. If the Protocol Specific Authentication Key
(Ks) is more than L octets long, then Ko is set to H(Ks). If the
Protocol Specific Authentication Key (Ks) is less than L octets long,
then Ko is set to the Protocol Specific Authentication Key (Ks) with
zeros appended to the end of the Protocol Specific Authentication Key
(Ks) such that Ko is L octets long.
For higher entropy it is RECOMMENDED that Key Ks should be at least L
octets long.
5.2. Computing the Hash
First, the Authentication Data field in the Cryptographic
Authentication TLV is filled with the value AuthTag. Then, to
compute HMAC over the Hello message it performs:
AuthData = HMAC(Ko, Hello Message)
Hello Message refers to the LDP Hello message excluding the IP and
the UDP headers.
5.3. Result
The resultant Hash becomes the Authentication Data that is sent in
the Authentication Data field of the Cryptographic Authentication
TLV. The length of the Authentication Data field is always identical
to the message digest size of the specific hash function H that is
being used.
This also means that the use of hash functions with larger output
sizes will also increase the size of the LDP message as transmitted
on the wire.
6. Processing Hello Message Using Cryptographic Authentication
6.1. Transmission Using Cryptographic Authentication
Prior to transmitting the Hello message, the Length in the
Cryptographic Authentication TLV header is set as per the
authentication algorithm that is being used. It is set to 24 for
HMAC-SHA-1, 36 for HMAC-SHA-256, 52 for HMAC-SHA-384 and 68 for HMAC-
SHA-512.
The Security Association ID field is set to the ID of the current
authentication key. The HMAC Hash is computed as explained in
Section 3. The resulting Hash is stored in the Authentication Data
field prior to transmission. The authentication key MUST NOT be
carried in the packet.
6.2. Receipt Using Cryptographic Authentication
The receiving LSR applies acceptability criteria for received Hellos
using cryptographic authentication. If the Cryptographic
Authentication TLV is unknown to the receiving LSR, the received
packet MUST be discarded according to Section 3.5.1.2.2 of [RFC5036].
The receiving LSR locates the LDP SA using the Security Association
ID field carried in the message. If the SA is not found, or if the
SA is not valid for reception (i.e., current time < KeyStartAccept or
current time >= KeyStopAccept), LDP Hello message MUST be discarded,
and an error event SHOULD be logged.
If the cryptographic sequence number in the LDP packet is less than
or equal to the last sequence number received from the same neighbor,
the LDP message MUST be discarded, and an error event SHOULD be
logged.
Before the receiving LSR performs any processing, it needs to save
the values of the Authentication Data field. The receiving LSR then
replaces the contents of the Authentication Data field with AuthTag,
computes the Hash, using the authentication key specified by the
received Security Association ID field, as explained in Section 3.
If the locally computed Hash is equal to the received value of the
Authentication Data field, the received packet is accepted for other
normal checks and processing as described in [RFC5036]. Otherwise,
if the locally computed Hash is not equal to the received value of
the Authentication Data field, the received packet MUST be discarded,
and an error event SHOULD be logged. The foresaid logging need to be
carefully rate limited, since while a LDP router is under attack of a
storm of spoofed hellos, the resource taking for logging could be
overwelming.
After the LDP Hello message has been successfully authenticated,
implementations MUST store the 64-bit cryptographic sequence number
for the Hello message received from the neighbor. The saved
cryptographic sequence numbers will be used for replay checking for
subsequent packets received from the neighbor.
7. Security Considerations
Section 1 of this document describes the security issues arising from
the use of unauthenticated LDP Hello messages. In order to address
those issues, it is RECOMMENDED that all deployments use the
Cryptographic Authentication TLV to authenticate the Hello messages.
The quality of the security provided by the Cryptographic
Authentication TLV depends completely on the strength of the
cryptographic algorithm in use, the strength of the key being used,
and the correct implementation of the security mechanism in
communicating LDP implementations. Also, the level of security
provided by the Cryptographic Authentication TLV varies based on the
authentication type used.
It should be noted that the authentication method described in this
document is not being used to authenticate the specific originator of
a packet but is rather being used to confirm that the packet has
indeed been issued by a router that has access to the Authentication
Key.
Deployments SHOULD use sufficiently long and random values for the
Authentication Key so that guessing and other cryptographic attacks
on the key are not feasible in their environments. In support of
these recommendations, management systems SHOULD support hexadecimal
input of Authentication Keys.
The mechanism described herein is not perfect . However, this
mechanism introduces a significant increase in the effort required
for an adversary to successfully attack the LDP Hello protocol while
not causing undue implementation, deployment, or operational
complexity.
8. IANA Considerations
The IANA is requested to as assign a new TLV from the "Label
Distribution Protocol (LDP) Parameters" registry, "TLV Type Name
Space".
Value Meaning Reference
----- -------------------------------- ------------------------
TBD1 Cryptographic Authentication TLV this document (sect 2.3)
The IANA is also requested to as assign value from the
"Authentication Cryptographic Protocol ID", registry under the
"Keying and Authentication for Routing Protocols (KARP) Parameters"
category.
Value MeaningDescription Reference
----- -------------------------------- ----------------------
TBD2 LDP Cryptographic Protocol ID this document (sect 4)
Note to the RFC Editor and IANA (to be removed before publication):
The new value should be assigned from the range 0x400 - 0x4ff using
the first free value.
9. Acknowledgements
We are indebted to Yaron Sheffer who helped us enormously in
rewriting the draft to get rid of the redundant crypto mathematics
that we had added here.
We would also like to thank Liu Xuehu for his work on background and
motivation for LDP Hello authentication. And last but not the least,
we would also thank Adrian Farrel, Eric Rosen, Sam Hartman, Stephen
Farrell, Eric Gray, Kamran Raza and Acee Lindem for their valuable
comments.
10. References
10.1. Normative References
[FIPS-180-3]
"Secure Hash Standard (SHS), FIPS PUB 180-3", October
2008.
[FIPS-198]
"The Keyed-Hash Message Authentication Code (HMAC), FIPS
PUB 198", March 2002.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4822] Atkinson, R. and M. Fanto, "RIPv2 Cryptographic
Authentication", RFC 4822, February 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, October 2009.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166, March 2014.
10.2. Informative References
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
[RFC5926] Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
for the TCP Authentication Option (TCP-AO)", RFC 5926,
June 2010.
[RFC6720] Pignataro, C. and R. Asati, "The Generalized TTL Security
Mechanism (GTSM) for the Label Distribution Protocol
(LDP)", RFC 6720, August 2012.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, May 2013.
Authors' Addresses
Lianshu Zheng
Huawei Technologies
China
Email: vero.zheng@huawei.com
Mach(Guoyi) Chen
Huawei Technologies
China
Email: mach.chen@huawei.com
Manav Bhatia
Alcatel-Lucent
India
Email: manavbhatia@gmail.com